In order to improve efficiency and realize mass production in the field of industrial manufacturing, programmable logic controllers (PLCs), personal computers (PCs), and single-chip microprocessors (SCMs) are generally applied in all kinds of industrial control circuits. However, PLCs are expensive, and the PCs are bulky. SCMs are best suited for use in an industrial control circuit, when the considerations of cost and bulk are paramount. In general, an SCM mainly includes an integrated circuit read-only memory (ROM) for program storage, an integrated circuit random-access memory (RAM) or scratch pad memory for alterable operand storage, and integrated circuit logic. In addition, an SCM may further include serial data communications, pulse modulated communications, eight bit instruction bytes, sixteen-bit operand words, shared input/output (I/O) channels, and/or other selected components.
As shown in FIG. 6, a typical industrial control circuit 10 includes an SCM 13, an interface circuit 14, a digital I/O circuit 18, and an analog I/O circuit 15. The analog I/O circuit 15 includes a digital to analog (D/A) conversion circuit 17 and an analog to digital (A/D) conversion circuit 16. The SCM 13 includes a computer, a RAM, a ROM (EPROM 2K×8), and twenty-seven I/O channels providing six digital signal bidirectional communication channels and eight analog signal bidirectional communication channels. In the illustrated industrial control circuit 10, the SCM 13 is an SCM8748 microprocessor. Alternatively, the SCM 13 may be an SCM8748, an SCM8749, an SCM8751, an SCM8048 or an SCM8049 microprocessor.
In operation, analog signals or digital signals may be input to the industrial control circuit 10 from an external circuit (not shown). If a digital signal is input, the digital I/O circuit 18 receives the digital signal and outputs the digital signal to the SCM 13 via an optoisolator 181. Then the SCM 13 generates a control signal according to the digital signal, and outputs the control signal to an external electrical device (not shown). If an analog signal is input, the analog I/O circuit 15 receives the analog signal, transforms the analog signal into a digital signal via the digital to analog (A/D) 16, and outputs the digital signal to the SCM 13. The SCM 13 generates a control signal according to the received digital signal, and outputs the control signal to the digital to analog (D/A) conversion circuit 17. The digital to analog (D/A) conversion circuit 17 transforms the digital signal into an analog signal, and outputs the analog signal to an external load (not shown) via the analog I/O circuit 15.
Because the industrial control circuit 10 only provides six digital signal bidirectional communication channels and eight analog signal bidirectional communication channels, the industrial control circuit 10 is not suitable for complicated communication in the field of industrial control. For example, the industrial control circuit 10 cannot synchronously deal with an application requiring sixteen-bit bidirectional communication.
It is desired to provide an industrial control circuit which overcomes the above-described deficiencies.